In the process of recovering certain trace metals present in fly ash from the combustion of coal, the fly ash is first treated in the presence of an oxidizing gas. Then the oxides are treated in the presence of a reducing gas to reduce the oxides to suboxides, which are volatile and consequently will sublime. Two valuable trace metals present in such fly ash are gallium and/or germanium. As described, these materials will sublime when reduced to their suboxides. The gaseous suboxides carried by the reducing gas are then caused to condense in order to remove the sublimate products from the reducing gas.
One method of removing the sublimation products, is to scrub the reducing gas with a cold liquid solution which will dissolve the suboxides. The solution is then evaporated to obtain the trace metals. Another method is to condense the suboxides on a cool surface, such as a "cold finger". A cold finger is an air-cooled probe which is introduced into the heated gaseous vapors. The cool exterior surface causes the suboxides to condense thereon, the reducing gas passing by the condenser after having "released" the suboxides. The condensation is then collected from the cooled surface and may be subjected to further processing.
However, air-cooled condensers have proved inefficient in the recovery of trace metal, such as germanium, which is very volatile when subjected to a reducing atmosphere. Nor have scrubbers provided an adequate solution.
It is therefore an object of the present invention to provide an improved collection system for the recovery of trace metals from fly ash.
Another object is to provide a collection system which operates efficiently without utilizing any coolant.
Yet another object of the invention is to provide a collection system which will efficiently recover sublimate products from volatile gases.
Another object of the invention present invention is to provide a collection system which is simple in operation and economical to manufacture.